Chemistry 1C-Dr. Larson
Chapter 20 Review Questions
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1) __________ is reduced in the following reaction:
Cr2O72- + 6S2O32- + 14H+ → 2Cr3+ + 3S4O62- + 7H2O
A) S4O62-
B) Cr2O72-
C) Cr3+
D) S2O32-
E) H+
2) Which substance is serving as the reducing agent in the following reaction?
14H+ + Cr2O72- + 3Ni → 3Ni2+ + 2Cr3+ + 7H2O
A) Ni
B) H2O
C) Cr2O72-
D) Ni2+
E) H+
3) __________ electrons appear in the following half-reaction when it is balanced.
S4O62- → 2S2O32A) 2
B) 4
C) 3
D) 1
E) 6
4) The balanced half-reaction in which dichromate ion is reduced to chromium(III) ion is a __________
process.
A) three-electron
B) six-electron
C) twelve-electron
D) four-electron
E) two-electron
5) The half-reaction occurring at the anode in the balanced reaction shown below is __________.
3MnO4- (aq) + 24H+ (aq) + 5Fe (s) → 3Mn2+ (aq) + 5Fe 3+ (aq) + 12H2O (l)
A) 2MnO4- (aq) + 12H+ (aq) + 6e- → 2Mn2+ (aq) + 3H2O (l)
B) Fe 2+ (aq) → Fe 3+ (aq) + eC) MnO4- (aq) + 8H+ (aq) + 5e- → Mn2+ (aq) + 4H2O (l)
D) Fe (s) → Fe 3+ (aq) + 3eE) Fe (s) → Fe 2+ (aq) + 2e-
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6) In a voltaic cell, electrons flow from the __________ to the __________.
A) anode, salt bridge
B) cathode, anode
C) anode, cathode
D) salt bridge, cathode
E) salt bride, anode
7) 1V = __________.
A) 1 amp · s
B) 1 J/C
C) 96485 C
D) 1 J/s
E) 1 C/J
8) The more __________ the value of E°red , the greater the driving force for reduction.
A) negative
B) extensive
C) endothermic
D) exothermic
E) positive
Table 20.2
Half-reaction
Cr3+ (aq) + 3e- → Cr (s)
Fe 2+ (aq) + 2e- → Fe (s)
Fe 3+ (aq) + e- → Fe 2+ (s)
Sn4+ (aq) + 2e- → Sn2+ (aq)
E° (V)
-0.74
-0.440
+0.771
+0.154
9) The standard cell potential (E°cell) for the voltaic cell based on the reaction below is __________ V.
Cr (s) + 3Fe 3+ (aq) → 3Fe 2+ (aq) + Cr3+ (aq)
A) -1.45
B) +1.51
C) +1.57
D) +2.99
E) +3.05
10) The standard cell potential (E°cell) of the reaction below is +0.126 V. The value of ΔG° for the reaction is
__________ kJ/mol.
Pb (s) + 2H+ (aq) → Pb 2+ (aq) + H2 (g)
A) -24
B) +24
C) -12
11) Galvanized iron is iron coated with __________.
A) phosphate.
B) magnesium.
C) iron oxide.
D) zinc.
E) chromium.
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D) +12
E) -50
12) Corrosion of iron is retarded by __________.
A) high pH conditions
B) the presence of salts
C) low pH conditions
D) both the presence of salts and high pH conditions
E) both the presence of salts and low pH conditions
13) How many minutes will it take to plate out 2.19 g of chromium metal from a solution of Cr3+ using a
current of 35.2 amps in an electrolyte cell __________ ?
A) 5.77
B) 17.3
C) 1.92
D) 346
E) 115
14) How many grams of CuS are obtained by passing a current of 12 A through a solution of CuSO4 for 15
minutes __________ ?
A) 3.6
B) 1.8
C) 14
D) 7.1
E) 0.016
D) (b) and (c)
E) (a) and (c)
15) Which of the following reactions is a redox reaction?
(a) K2CrO4 + BaCl2 → BaCrO4 + 2KCl
(b) Pb 22+ + 2Br- → PbBr
(c) Cu + S → CuS
A) (a) only
B) (b) only
C) (c) only
16) Which transformation could take place at the anode of an electrochemical cell?
A) F 2 toF B) Cr2O72- → Cr2+
C) O2 to H2O
D) HAsO2 to As
E) None of the above could take place at the anode.
17) The purpose of the salt bridge in an electrochemical cell is to __________.
A) maintain electrical neutrality in the half-cells via migration of ions.
B) provide a means for electrons to travel from the cathode to the anode.
C) provide oxygen to facilitate oxidation at the anode.
D) provide a means for electrons to travel from the anode to the cathode.
E) provide a source of ions to react at the anode and cathode.
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18) Which transformation could take place at the cathode of an electrochemical cell?
A) Br2 → BrO3B) NO → HNO2
C) HSO4- → H2SO3
D) MnO2 → MnO4E) Mn2+ → MnO419) Which one of the following types of elements is most likely to be a good oxidizing agent?
A) halogens
B) alkaline earth elements
C) lanthanides
D) transition elements
E) alkali metals
20) Which one of the following is the best oxidizing agent ?
A) Na
B) H2
Table 20.1
Half Reaction
F 2 (g) + 2e- → 2F - (aq)
Cl2 (g) + 2e- → 2Cl- (aq)
Br2 (l) + 2e- → 2Br- (aq)
O2 (g) + 4H+ (aq) + 4e- → 2H2O (l)
Ag + + e- → Ag (s)
Fe 3+ (aq) + e- → Fe 2+ (aq)
I2 (s) + 2e- → 2I- (aq)
Cu2+ + 2e- → Cu (s)
2H+ + 2e- → H2 (g)
Pb 2+ + 2e- → Pb (s)
Ni2+ + 2e- → Ni (s)
Li+ + e- → Li (s)
C) O2
D) Ca
E) Li
D) Br2 (l)
E) Ni2+ (aq)
E°(V)
+2.87
+1.359
+1.065
+1.23
+0.799
+0.771
+0.536
+0.34
0
-0.126
-0.28
-3.05
21) Using Table 20.1, which substance can oxidize I- (aq) to I2 (s) ?
A) Cu2+ (aq)
B) Br- (aq)
C) Ag (s)
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Table 20.2
Half-reaction
Cr3+ (aq) + 3e- → Cr (s)
Fe 2+ (aq) + 2e- → Fe (s)
Fe 3+ (aq) + e- → Fe 2+ (s)
Sn4+ (aq) + 2e- → Sn2+ (aq)
E° (V)
-0.74
-0.440
+0.771
+0.154
22) Which of the following reactions will occur spontaneously as written?
A) 3Sn4+ (aq) + 2Cr (s) → 2Cr3+ (aq) + 3Sn2+ (aq)
B) 3Fe 2+ (aq) → Fe (s) + 2Fe 3+ (aq)
C) Sn4+ (aq) + Fe 3+ (aq) → Sn2+ (aq) + Fe 2+ (aq)
D) Sn4+ (aq) + Fe 2+ (aq) → Sn2+ (aq) + Fe (s)
E) 3Fe (s) + 2Cr3+ (aq) → 2Cr (s) + 3Fe 2+ (aq)
23) Consider an electrochemical cell based on the reaction:
2H+ (aq) + Sn (s) → Sn2+ (aq) + H2 (g)
Which of the following actions would change the measured cell potential?
A) increasing the [Sn2+] in the anode compartment
B) increasing the pressure of hydrogen gas in the cathode compartment
C) lowering the pH in the cathode compartment
D) increasing the pH in the cathode compartment
E) Any of the above will change the measure cell potential.
24) Consider an electrochemical cell based on the reaction:
2H+ (aq) + Sn (s) → Sn2+ (aq) + H2 (g)
Which of the following actions would not change the measured cell potential?
A) lowering the pH in the cathode compartment
B) increasing the pressure of hydrogen gas in the cathode compartment
C) addition of more tin metal to the anode compartment
D) increasing the tin (II) ion concentration in the anode compartment
E) Any of the above will change the measured cell potential.
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25) Cathodic protection of a metal pipe against corrosion usually entails
A) attaching an active metal to make the pipe the anode in an electrochemical cell.
B) coating the pipe with another metal whose standard reduction potential is less negative than that of
the pipe.
C) attaching a dry cell to reduce any metal ions which might be formed.
D) coating the pipe with a fluoropolymer to act as a source of fluoride ion (since the latter is so hard to
oxidize).
E) attaching an active metal to make the pipe the cathode in an electrochemical cell.
26) One of the differences between a voltaic cell and an electrolytic cell is that in an electrolytic cell __________.
A) electrons flow toward the anode
B) a nonspontaneous reaction is forced to occur
C) O2 gas is produced at the cathode
D) oxidation occurs at the cathode
E) an electric current is produced by a chemical reaction
27) The standard cell potential (E°) of a voltaic cell constructed using the cell reaction below is 0.76 V:
Zn (s) + 2H+ (aq) → Zn 2+ (aq) + H2 (g)
With PH2 = 1.0 atm and [Zn 2+] = 1.0 M, the cell potential is 0.66 V. The concentration of H+ in the cathode
compartment is __________ M.
A) 2.0 × 10 -2
B) 1.0 × 10 -12
C) 4.9 × 10 1
D) 4.2 × 10 -4
E) 1.4 × 10 -1
28) A voltaic cell is constructed with two silver-silver chloride electrodes, where the half-reaction is
AgCl (s) + e- → Ag (s) + Cl- (aq)
E° = +0.222 V
The concentrations of chloride ion in the two compartments are 0.0222 M and 2.22 M, respectively. The cell
emf is __________ V.
A) 0.232
B) 0.118
C) 22.2
D) 0.212
E) 0.00222
29) The standard emf for the cell using the overall cell reaction below is +2.20 V:
2Al (s) + 3I2 (s) → 2Al 3+ (aq) + 6I- (aq)
The emf generated by the cell when [Al 3+] = 4.5 × 10-3 M and [I-] = 0.15 M is ________ V.
A) 2.39
B) 2.20
C) 2.23
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D) 2.30
E) 2.10
30) The town of Natrium, West Virginia, derives its name from the sodium produced in the electrolysis of
molten sodium chloride (NaCl) mined from ancient salt deposits. The number of kilowatt-hours of
electricity required to produce 4.60 kg of metallic sodium from the electrolysis of molten NaCl(s) is
__________ when the applied emf is 4.50 V.
A) 0.0241
B) 24.1
C) 12.1
D) 0.0414
E) 48.3
31) The electrolysis of molten AlCl 3 for 3.25 hr with an electrical current of 15.0 A produces __________ g of
aluminum metal.
A) 16.4
B) 147
C) 49.1
D) 0.606
E) 4.55 × 10-3
SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
32) In the formula ΔG = -nFE , F is the __________.
33) The dependence of cell emf on concentration is expressed in the __________ .
34) A voltaic cell can be constructed of the same species as long as the __________ are different.
35) The potential (E) to move K+ from the extracellular fluid to the intracellular fluid necessitates work. The
sign for this potential is __________.
36) The major product of a hydrogen fuel cell is __________.
37) When iron is coated with a thin layer of zinc to protect against corrosion, the iron is said to be __________ .
38) The quantity of charge passing a point in a circuit in one second when the current is one ampere is called a
__________ .
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
39) The standard reduction potential, E o
red , is proportional to the stoichiometric coefficient.
40) In a half reaction the amount of a substance that is reduced or oxidized is directly proportional to the
number of electrons generated in the cell.
41) The standard reduction potential of X is 1.23 V and that of Y is -0.44 V therefore X is oxidized by Y.
42) A positive number for maximum useful work in a spontaneous process (voltaic cell) indicates that the cell
will perform work on its surroundings.
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Answer Key
Testname: CHAPTER 20 QUIZ
1) B
Page Ref: Sec. 20.1
2) A
Page Ref: Sec. 20.1
3) A
Page Ref: Sec. 20.2
4) B
Page Ref: Sec. 20.2
5) D
Page Ref: Sec. 20.3
6) C
Page Ref: Sec. 20.3
7) B
Page Ref: Sec. 20.4
8) E
Page Ref: Sec. 20.4
9) B
Page Ref: Sec. 20.4
10) A
Page Ref: Sec. 20.5
11) D
Page Ref: Sec. 20.8
12) A
Page Ref: Sec. 20.8
13) A
Page Ref: Sec. 20.9
14) A
Page Ref: Sec. 20.9
15) C
Page Ref: Sec. 20.1
16) E
Page Ref: Sec. 20.3
17) A
Page Ref: Sec. 20.3
18) C
Page Ref: Sec. 20.3
19) A
Page Ref: Sec. 20.4
20) C
Page Ref: Sec. 20.4
21) D
Page Ref: Sec. 20.4
22) A
Page Ref: Sec. 20.5
23) E
Page Ref: Sec. 20.6
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Answer Key
Testname: CHAPTER 20 QUIZ
24) C
Page Ref: Sec. 20.6
25) E
Page Ref: Sec. 20.8
26) B
Page Ref: Sec. 20.9
27) A
Page Ref: Sec. 20.6
28) B
Page Ref: Sec. 20.6
29) D
Page Ref: Sec. 20.6
30) B
Page Ref: Sec. 20.9
31) A
Page Ref: Sec. 20.9
32) Faraday constant or the charge on one mole of electrons
Page Ref: Sec 20.5
33) Nernst equation
Page Ref: Sec 20.6
34) concentrations
Page Ref: Sec 20.6
35) negative
Page Ref: Sec 20.6
36) water
Page Ref: Sec 20.7
37) galvanized
Page Ref: Sec 20.7
38) coulomb
Page Ref: Sec 20.9
39) FALSE
Page Ref: Sec 20.4
40) TRUE
Page Ref: Sec
20.9
41) FALSE
Page Ref: Sec 20.8
42) FALSE
Page Ref: Sec 20.9
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